Concrete form surfacing

ABSTRACT

There is disclosed herein a method for preparation and construction of concrete pouring forms in which the surfaces and edges of the form members are treated with several coats of a resinous material exhibiting particularly advantageous mechanical and chemical properties. A preferred material is a moisture cured urethane prepolymer solution.

Elite? Sites Willingh 1 Mar. 21, 1972 154] CONCRETE FORM SURFACENG [72]Inventor: John 111. Willingham, 1280 Estate Drive,

Memphis, Tenn. 38117 [22] Filed: Jan.27, 1969 [21] Appl.No.: 794,227

[52] U.S. Cl ..1l1l7/5.l,117/5.3,117/68,

117/72, 117/126 GB, 117/132 B, 117/148, 117/161 KP, 249/189, 252/305,264/338 ..B29c l/04 ..l17/5.l, 161 KP, 68, 53,132 B,

I51] Int. [58] Field ofSearc [56] References Cited UNITED STATES PATENTS2,753,276 7/1956 Brochhagen et a1. ..117/161X 2,987,494 6/1961 Black ..117/161 X 3,240,618 3/1966 Flemming, ..1 17/51 3,389,008 6/1968 Bailey..117/148 3,427,178 2/1969 Zakim et a] ..l l7/5.1 3,505,252 4/1970Brotherton et al ..1 17/161 X Primary Examiner-William D. MartinAssistant Examiner-Mathew R P Perrone, Jr. Attorney-Le Blanc & Shur [57] ABSTRACT 7 Claims, 1 Drawing Figure Patented March 21, 1972 INVENTORJOHN H. WILLINGHAM ATTORNEYS CONCRETE FORM SURFACING BACKGROUND OF THEINVENTION This invention relates to the preparation and construction offorms used for concrete casting, and more particularly to the use of aresinous coating material on the forms to provide greater durability,increased and usable lifetime, and an extremely smooth and uniformsurface on the finished concrete product.

Use of forms for casting concrete structures such as wall panels,facades, decking, etc. is well known in the construction industry. Suchforms are ordinarily constructed of panel members formed of wood, steel,etc. to provide the concrete forming surface, and of suitable supportingand spacing structure or framing. Ordinarily, wood panels are preferredsince wood forms are often less expensive to manufacture and easier tohandle due to lighter weight. However, there are several significantdisadvantages. For example, the forms are reused many times over in thecourse of a construction project, but the wood panels rapidly absorbmoisture in use. This causes panel surface deterioration and buckling orwarpage. Frequent replacement is therefore necessary to assure a flatand uniform surface on the cast concrete product.

Use of steel form panels overcomes several of the above noteddisadvantages, particularly the limited durability of the wood panels.Steel is therefore preferred for extremely large projects or permanentinstallations, However, the steel forms are heavier and often morecostly. Also, they are subject to surface deterioration due to rusting,corrosion, etc.

In recognition of these problems, it has been proposed to improve thedurability of wood form panels by coating them with a suitablewaterproof plastic. However, such efforts were not completelysatisfactory.

In a further effort to overcome these disadvantages, it has beenproposed to use a composite panel structure employing a central core ofwood or other material with built-up composite faces formed offiberglass reinforced polyester resin. Such forms may be more durablethan forms currently in use, but are also subject to several seriousdisadvantages. Construction of even simple forms in this manner isrelatively complex and costly, and requires utilization of skilledlabor. Moreover, such forms can ordinarily not be built at theconstruction site, but must be prefabricated elsewhere and trucked tothe site for assembly. Further, while the panels are relatively durable,they are subject to damage in use, for example, while the finishedconcrete panel is being removed from the form. The forms are quitedifficult to repair, again, requiring skilled labor. As a result,fiberglass reinforced polyester forms are not in use commercially andhave not gained acceptance, insofar as applicant is aware.

SUMMARY OF THE INVENTION In accordance with the present invention, ithas been found that the disadvantages of uncoated wood forms and of theheretofore proposed alternatives can be overcome, and form panels can bemanufactured in a simple and inexpensive manner by utilization ofmaterials having certain quite specific properties. Forms made accordingto this invention are durable and may be reused many times, yet they areeasily manufactured at the construction site by unskilled workmen. Formsconstructed in accordance with this invention have an additionaladvantage in that the usual form release compositions employed tofacilitate separation of the concrete product from the forms may bedispensed with, except for occasional application.

Also, because of the smooth and uniform surface against which theconcrete is poured, the resulting product possesses an extremely smoothand uniform surface. In this regard, it has been found quitesurprisingly that the concrete surface is so smooth and glossy that itreflects light without substantial diffusion. This property may be ofdecorative value in some instances, but if desired, the surface may beconveniently treated by sand blasting or otherwise to remove the highsurface gloss.

In accordance with the invention, the improved form panel is made bycoating a core member formed of wood, steel, or fiberglass with aresinous material having certain particular properties. After suitablecuring, a second (and in the case of wood core members) a third coatingis applied. After final curing, the panel is ready for use in theassembly of form structures of any desired type.

Coating materials found to be suitable are air or moisture curableresins capable of being thinned to low viscosity for convenientapplication. In the cured state the coating material should exhibit highhardness and tensile strength. good impact and abrasion resistance, andnegligible water absorption. Sur prisingly, materials having therequisite properties have been available for some time without industryrecognition of their efficacy for the present purpose.

Accordingly, an object of this invention is to provide a new surfacetreatment for, concrete form panels, and to produce such panels havingsubstantially increased durability and extended useful lifetime.

Another object of this invention is to provide a simple and inexpensivetechnique for construction of concrete forms, whereby the forms may bebuilt by relatively unskilled laborers directly at the constructionsite. A related object is to provide improved concrete pouring forms,which may readily be repaired at the construction site by unskilledlabor.

It is also an object of this invention to provide a concrete pouringform which does not require use of a form release compound on theconcrete forming surfaces after each use.

It is a further object of this invention to provide a concrete pouringform which may be utilized to produce concrete having an extremelysmooth or glossy and uniform surface.

The exact nature of the invention, as well as other objects andadvantages thereof will be apparent from consideration of the followingdetailed description, and the accompanying drawing in which the singleFIGURE shows a simple form panel constructed in accordance with thisinvention.

DETAILED DESCRIPTION Referring now to the drawing, there is illustrateda form panel member 6 manufactured according to the present invention.The composite panel includes a core member 8 which may be formed ofwood, steel, fiberglass or other suitable material. Core member 8 iscoated on all sides and edges with a resinous material having particularproperties as specified hereinafter.

For most applications, core member 8 is made of wood, preferablyone-fourth to 1 inch plywood. Low grade plywood panels, e.g., grade BB,may be employed since the applied coating provides a smooth and uniformsurface even on the rough and nonuniform plywood. As illustrated, on awood core 8, there are provided several coats of resinous material,e.g., three coats, as indicated at I0, 12 and 14. Best results areachieved if both sides and all edges of the core member are coated withthe resinous material. The coating may be applied in any suitablefashion, e.g., by dipping (immersion) brushing, rolling, or spraying.Due to the advantageous properties of the resinous material, each coatmay be relatively thin, e.g.. 3-6 mils. On wood core members, a minimumof three coats should be employed to provide the desired durability, andto prevent buckling and/or warping of the panel. The inner coat 10 ispreferably diluted approximately 50 percent with solvent to reduced thesolids concentration, and to promote absorption into the wood surface,whereby this coat serves as a primer. When applied to metal or othernonabsorptive materials, the diluted inner layer may be dispensed with.

After the panel has been coated in the manner hereinafter described, itmay be employed in the construction of any conventional or desired typeof form. Thus, this invention is applicable to simple forms used forpoured-in-place slabs. vertical wall panels or even complex frames ordecorative facades. In the latter case, form preparation according tothis invention is of special value since the resulting concrete surfaceis smooth and uniform even if the actual surface profile is quitecomplex. However, since the detailed nature of the form itself does notconstitute a part of this invention, a description of typical formconstructions is omitted in the interest ofbrevity.

As pointed out above, essential to the success of this invention is theemployment of a resinous coating material having certain specialproperties. Specifically, it has been found that the coating materialmust be such that the cured coating possesses high hardness withoutbrittleness, high tensile strength, and impact resistance, virtuallynegligible water absorption, and high resistance to abrasion.

More specifically, it has been found that resinous materials appropriateto the practice of this invention should produce a cured coating whichexhibits a minimum tensile strength of between 2,000 and 5,000 p.s.i.,elongation between about 20-150 percent, hardness (Sward) between about30 and 60, Taber Abrasion weight loss (CSlO wheel, 1,000 g. wt. 1,000cycles) not exceeding about 75 mg., and minimum impact re sistance(Gardner) of 140 in.-lbs.'(direct and reverse). In the' uncured state,the resinous material should not exhibit a viscosity (Brookfield)significantly exceeding about l50l60 c.p.s. or a specific gravitysignificantly exceeding about 0.95-1.0.

While materials exhibiting the foregoing combination of propertiesare'not common, there are a number of highly suitable materialsavailable. These include single component resin systems such as aircured urethane oils (isocyanate modified drying oils) and moisturecurable isocyanate terminated urethane prepolymers. Heat curableurethane resins (single component) may also be suitable, but do not lendthemselves to convenient use at the construction site. Likewise, twocomponent systems including catalysts may be suitable but lessconvenient.

One particularly satisfactory material is a moisture cured aromaticdiisocyanate prepolymer known as Neorez U 105, distributed by PolyvinylChemicals Inc., Wilmington, Mass. Using this material, a cured coating(thickness 3 mils) may be produced having properties as set forth inTable I below:

Tensile Strength Elongation 7000 p.s.i. Hardness (Sward):

1 day 24 Ultimate 45 Impact Resistance Direct l60 inch-lb. Reverse l40inch-lb. Taber Abrasion (CSlO wheel,

1000 g. load, I000 cycles) 23 mg.

TABLE I: Film Properties of Preferred Resinous Material By virtue ofthese properties the described prepolymer is the preferred coatingmaterial, but it will be understood that other materials exhibitingcomparable properties may also be employed. For example, a similarmaterial can be obtained from the C. P. Hall Chemical Company ofChicago, Illinois or Cook Paint and Varnish Company, Kansas City,Missouri.

Liquid coating materials exhibiting the above properties should also besusceptable to solvent thinning or other viscosity adjustment to permitapplication to the form panels by dipping, brushing, rolling, orspraying. For the urethane prepolymer materials described this can beaccomplished by use of xylene, Cellosolve acetate (ethylene glycolmonoethyl ether acetate) or mixtures thereof.

Further in this regard, it should be noted that the solids concentrationof the liquid coating material is directly related to the durability.However, excessive solids concentration is unsatisfactory since highviscosity results, preventing satisfactory application to the coremembers. In particular, for the materials suitable for use according tothis invention, it has been determined that the solids concentration andviscosity vary in the manner set forth in Table II below:

Solids Concentration Viscosity (Brookfield) cps.

TABLE II: Variation of Viscosity with Solids Content Best results areobtained for coating by brushing, rolling or dipping at a viscosity ofabout -160 c.p.s. while spraying is best accomplished at a viscosity ofabout 100 c.p.s. Thus thinning to solids concentrations of 40 percentfor brushing, etc. or 30-35 percent for spraying, yields best results.

In addition to the foregoing, certain other requirements for properapplication of the coating material to the form panels, curing, etc.should be observed for best results. The following examples illustratethe manner in which all requirements should be met in successfulpractice of this invention. 7

EXAMPLE I A plywood board, three-fourths inch, grade BB is cut to theproper size and shape. A moisture curable, urethane prepolymerexhibiting film properties as set forth in Table I, and having a solidsconcentration of approximately 40 percent, a viscosity of l50 c.p.s. isxylene thinned 50 percent to reduce solids concentration. The thinnedprepolymer solution is applied to all surfaces and edges of the plywoodcore member as a primer coat. This may be done by dipping, brushing, orrolling as desired. The coated core member is then cured in air forapproximately 3 to 4 hours under conditions of at least 50 percentrelative humidity. Then, second and third coats of unthinned prepolymersolution (40 percent solids, 150 c.p.s. viscosity) are applied to theonce-coated core member, again by brushing, rolling, or dipping. Thesecond and third coats are each air cured in the manner previouslydescribed. The composite form panel is then ready for use in a form ofany desired design. Plywood form panels prepared in the manner describedcan be used one hundred or more times without significant surface orstructural deterioration EXAMPLE 2 A steel plate (7 gauge) issandblasted or otherwise treated and then cleaned to produce a rough,generally uniform surface. The urethane prepolymer solution described inExample 1 is solvent thinned to a 30 to 35 percent solids concentration.At least two coats of the prepolymer solution are sprayed onto the plateon both sides and all edges. After each application, the coating is aircured as in Example l. The result is an ultradurable, rustproof concreteform panel usable well in access of one hundred times withoutresurfacing. When necessary, the panel may be sandblasted and recoated.The panel so treated is found to be completely renewed and ready foruse.

EXAMPLE 3 A fiberglass core member is precast in any desired surfaceconfiguration to produce a forming surface usable in the casting ofdecorated facade panels, etc. The durability of such panels may also beenhanced according to this invention. Thus, the fiberglass surface issanded or otherwise roughened. Two coats of a polyurethane coatingsolution exhibiting film properties as set forth in Table I is thinnedto a viscosity of approximately l50 c.p.s. and applied to the fiberglasscore member by dipping, rolling, or brushing. Each coat is cured untilhard. In this way, a highly durable form member may be produced havingan extremely smooth and uniform surface. The form member so treated maybe used to form intricate surface patterns without the necessity of formrelease compounds.

EXAMPLE 4 As noted above, a particular advantage of the form panelsmanufactured in accordance with this invention is the amenability torapid and effective repair by unskilled personnel.

Thus, in the event that a panel prepared as in Examples 1-3 has beendamaged, e.g., from impact with the cast concrete product during removalfrom the forms, the affected portion can be repaired as follows: thedamaged area is rough-sanded, and deep scars in the core member arebuilt up with a suitable filler composition e.g., a compatibleepoxy-type filler). The affected area is leveled by sanding and cleaned.The area is then recoated as described above with two or three coats ofthe coating material and each coat is cured. A damaged panel iscompletely renewable in this manner.

As may be seen from the foregoing, several variations in the appropriateprocedure may be possible. Also, in Example I, use of a moisture cured,urethane prepolymer under dry conditions, for example, below about 50percent relative humidity, may be unsatisfactory since the curing timeis substantially lengthened, and, in the case of extremely low humidity,curing is completely inhibited. Under such conditions, air curedurethane-modified drying oil compositions or other materials exhibitingproperties as set forth herein should be substituted. Alternatively, across-linker, for example, a polyhydroxy amine such as sold under thename Quadrol by Wyandotte Chemical Corporation may be added to theprepolymer in a concentration of about 2 to 4 oz. per gallon for curingat a relative humidity between about 30 and 50 percent. For relativehumidity substantially below about 30 percent, 6 oz. of cross-linker pergallon of prepolymer solution may be employed.

Further, under low temperature conditions, the curing time for theprepolymer is increased. To overcome this, a suitable acceleratorcompatible with the particular urethane prepolymer may be employed.

As an additional extension of the present concepts, it is contemplatedthat form surface repair can be facilitated by preparing the liquidresinous material in aerosol form with a conventional compatiblepropellant. This would permit convenient on-the-spot repair of minordamage. As will be appreciated, the various mechanical propertiesdescribed herein should be observed in selection of the resinousmaterial for aerosol packaging. Again, however, the moisture curableisocyanate terminated prepolymer is preferred.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresent embodiment is therefore to be considered in all respects asillustrative and not restrictive, the scope ofthe invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

l. A method of making a rigid form member with a cured, single componentresin coated exterior for a concrete pouring form having surfacecharacteristics of tensile strength of at least 2,000 to 5,000 p.s.i.,hardness (Sward) between about 30 and 60, impact resistance (Gardner) ofat least about 140 in. lbs. direct and reverse, and Taber Abrasion (CSlOwheel, 1,000 grams, l,000 cycles) maximum weight loss of less than 75milligrams, which comprises:

providing a wooden core member having a preselected shape anddimensional configuration;

applying a first coating to all surfaces of said core member,

said coating consisting of a moisture curable, isocyanateterminated,urethane prepolymer in a solvent, having a solids concentration ofapproximately 20 percent and a viscosity (Brookfield) ofless than c.p.s.

exposing said coated surfaces to ambient atmospheric moisture for aperiod sufficient to cure said coating;

subsequently, applying a plurality of additional coatings to allsurfaces of said member; each of said additional coatings consisting ofthe said urethane prepolymer in a solvent having a solids concentrationof about 30 percent to about 40 percent and a viscosity (Brookfield) notexceeding approximately 1 5O c.p.s. successively exposing said coatedsurfaces to ambient atmospheric after each of said coatings is appliedfor a period sufficient to cure said coating before each additionalcoating is applied.

2. The method of claim] wherein the wooden core member is plywood.

3. The method of claim 1 wherein the solvent is at least one memberselected of the group consisting of xylene and ethylene glycol monoethylether acetate.

4. The method of claim 1 wherein the curing period is from 3 to 4 hoursin relative humidity of greater than 50 percent.

5. A method of making a rigid form member with a cured, singlecomponent, resin coated exterior for a concrete pouring form havingsurface characteristics of tensile strength of at least 2,000 to 5,000p.s.i., hardness (Sward) between about 30 and 60, impact resistance(Gardner) of at least about in. lbs. direct and reverse, and TaberAbrasion (CSlO wheel, 1,000 grams, 1,000 cycles) maximum weight loss ofless than 75 milligrams which comprises:

providing a core member having a preselected shape and dimensionalconfiguration, said core comprising steel, wood, or fiberglass; applyinga first coating to all surfaces of said core member,

said coating consisting of a moisture curable, isocyanateterminated,urethane prepolymer in a solvent having a solids concentration ofapproximately 50 percent of the solids concentration of subsequentlyapplied coatings and a viscosity (Brookfield) of less than approximatelyc.p.s.

exposing said coated surfaces to ambient atmospheric moisture for aperiod sufficient to cure said coating;

subsequently applying at least one additional coating to all surfaces ofsaid member; said additional coating consisting of the said urethaneprepolymer in a solvent having a solids concentration of about 30percent to about 40 percent and a viscosity (Brookfield) ofapproximately l50 c.p.s.

successively exposing said additionally coated surface to ambientatmospheric moisture for a period sufficient to cure said coating.

6. The method of claim 5 wherein the solvent is at least one memberselected from the group consisting of xylene and ethylene glycolmonoethyl ether acetate.

7. The method of claim 5 wherein the curing period is from 3 to 4 hoursin relative humidity not greater than about 50 per cent.

2. The method of claim 1 wherein the wooden core member is plywood. 3.The method of claim 1 wherein the solvent is at least one memberselected of the group consisting of xylene and ethylene glycol monoethylether acetate.
 4. The method of claim 1 wherein the curing period isfrom 3 to 4 hours in relative humidity of greater than 50 percent.
 5. Amethod of making a rigid form member with a cured, single component,resin coated exterior for a concrete pouring form having surfacecharacteristics of tensile strength of at least 2, 000 to 5,000 p.s.i.,hardness (Sward) between about 30 and 60, impact resistance (Gardner) ofat least about 140 in. lbs. direct and reverse, and Taber Abrasion (CS10wheel, 1,000 grams, 1,000 cycles) maximum weight loss of less than 75milligrams which comprises: providing a core member having a preselectedshape and dimensional configuration, said core comprising steel, wood,or fiberglass; applying a first coating to all surfaces of said coremember, said coating consisting of a moisture curable,isocyanate-terminated, urethane prepolymer in a solvent having a solidsconcentration of approximately 50 percent of the solids concentration ofsubsequently applied coatings and a viscosity (Brookfield) of less thanapproximately 150 c.p.s. exposing said coated surfaces to ambientatmospheric moisture for a period sufficient to cure said coating;subsequently applying at least one additional coating to all surfaces ofsaid member; said additional coating consisting of the said urethaneprepolymer in a solvent having a solids concentration of about 30percent to about 40 percent and a viscosity (Brookfield) ofapproximately 150 c.p.s. successively exposing said additionally coatedsurface to ambient atmospheric moisture for a period sufficient to curesaid coating.
 6. The method of claim 5 wherein the solvent is at leastone member selected from the group consisting of xylene and ethyleneglycol monoethyl ether acetate.
 7. The method of claim 5 wherein thecuring period is from 3 to 4 hours in relative humidity not greater thanabout 50 percent.